There are numerous proposed schemes by which various natural ores, concentrates and slags may be processed for the recovery of metal values. One commercial scheme for the extraction and separation of tantalum and columbium (also known as niobium) values from beneficiated ores or from the widely available tin slags, is described in detail in U.S. Pat. Nos. 2,767,047; 2,953,453; 2,962,372; 3,117,833; 3,300,297; 3,658,511; 3,712,939 and 4,164,417. In this process, feed solids are digested with hot, concentrated hydrofluoric acid to solubilize most of the tantalum and columbium values as fluorides. A liquor containing the dissolved metal values is separated from a waste sludge and treated in a multistage liquid-liquid extraction cascade wherein the metal values are extracted with methylisobutyl ketone (MIBK). The waste sludge from this process still contains insolubles such as uranium and thorium and also contains within the entrained insolubles significant amounts of dissolved tantalum and columbium (about 1-5% by weight of each). Disposal of uranium and thorium is regulated by the Nuclear Regulatory Commission (NRC). Presently, the bulk of this waste sludge is being stockpiled at the ore processing facilities because of the difficulty in recovering the small amounts of remaining metal values, resulting in an ever growing disposal problem as well as lost revenues from the unrecovered metal values.
A general discussion of other ore process schemes is found in Extractive Metallurgy of Niobium, Tantalum and Vanadium, INTERNATIONAL METALS REVIEW, 1984, Vol. 29, No. 26, BB 405-444, published by The Metals Society (London).